Tyre Pressure - Too High or Too Low?

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Robert Clark

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The recommended tyre pressures for my MH (according to the Manufacturer) are 5.5 bar front and rear, based on the tyre size that I have

The max tyre pressure written on the tyre is 5.5 bar

The dealer suggests 3.4 - 3.8 bar for the front and 4.1 to 4.5 bar for the rear, as they feel that the ride is a too 'hard' otherwise.

I understand that low tyre pressure can affect handling and fuel consumption

Who is right, the dealer or the manufacturer?
 
Manufacturer. But depends upon laden weight also. It should not deviate that much. 0.5 bar less for front is normally okay with high pressures. Tyres too low will mean extra heat and more chance of blowing out. It also stresses the side wall more, because there is more flexing, less stability because the vehicle is moving more on the tyre, more chance of damage. I am sure there will be contradictions coming though...
 
MyDogsTooBig said:
Manufacturer. But depends upon laden weight also. It should not deviate that much. 0.5 bar less for front is normally okay with high pressures. Tyres too low will mean extra heat and more chance of blowing out. It also stresses the side wall more, because there is more flexing, less stability because the vehicle is moving more on the tyre, more chance of damage. I am sure there will be contradictions coming though...
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Would the lower pressure affect steering and handling too?
 
Manufacturer. Dealer probably has the experience of running the vehicle at those px but the manufacturers have the tech knowledge for the weights etc.
 
I would trust any motor home dealers.
For all the money we spend with them for 'expert service and advise' they still seem to be a bloody cottage industry.

Its good job we can depend on expert advice from forum members that have genuine knowledge of motor homes.

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The front is more susceptible to incorrect tyre pressures. Low tyres will help it track straight, so steering is dulled down (less wander or wobble with undulations and wind), but that then makes turning more difficult, because it will want to keep straight. For the backs, the turning effect is less of an issue, but it is usually where most of the weight is. Low tyres for the backs will reduce harsh bounce and reduce wander in winds. The problem is, that because the weight is in the back, low tyres at the back will increase tyre wear and stresses and generate more heat, which is not what you want. Tyre wall maximum pressures are just that and are a guide. You should however be near the guide, not nearly half of it. I adjusted my rears depending upon weight, but only by 0.5 bar. If you are tactile, you will feel what is not good with tyre pressures and be able to adjust them. If you have a lot of sway and weight at the back, then air bags give good correction and are easily adjusted by air pressure for differing loads weights, which is what I did when carrying water when I had no choice. If your steering is twitchy and you have to correct it a lot as you drive, then a lower tyre pressure will correct this to an extent, but only go down a small amount in pressure. If the problem persists, then check toe in/out and/or think of fitting a steering damper.
 
Robert Clark said:
The recommended tyre pressures for my MH (according to the Manufacturer) are 5.5 bar front and rear, based on the tyre size that I have

The max tyre pressure written on the tyre is 5.5 bar

The dealer suggests 3.4 - 3.8 bar for the front and 4.1 to 4.5 bar for the rear, as they feel that the ride is a too 'hard' otherwise.

I understand that low tyre pressure can affect handling and fuel consumption

Who is right, the dealer or the manufacturer?
Click to expand...
What tyres have you got? The only way to really find what pressure they should be at is to ask the tyre manufacturer, not the vehicle manufacturer or the dealer.

In order to find the right pressure you will to take the laden MH to a weighbridge and determine the axle weights.

If you have Continental tyres there are charts you can look up. I now run my tyres at a much lower pressure than the vehicle handbook says but the pressures are spot on by Continental and the ride is much better.
 
No technical skill on my part, but I would not be comfortable running the tyres at the maximum recommended pressure :), always like to see some margin (y)
 
I would go with the dealers figures, max pressure would go with max load.

Martin

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@Robert. Get the van weighed if you haven't already and then email Continental with the tyre type and size and loaded weights for front and rear axles.

www.continental-tyres.co.uk for more info.

They will give you the correct pressures.

Not sure which van you have but I've recently emailed Michelin for my pressures and have been told to keep 80psi in the rear and 51psi front.
That's for a Carthago Chic C-Line with a max weight of 4500kg.

Richard.
 
I have tyrepal on my tag axle and when I set the rears to 70psi (Michelin Agilis) when they get up to temperature on a run the pressure goes up to about 80psi, when in Spain last year they got up to 85 psi. It's a similar ratio with the fronts. The tyre temps are not excessive maybe 30-35 ish dregs. .......so......when the manufacturers/dealers say to set them to 80psi does this take into account the running pressures??? Or does it not matter?...

I should say this is on a warm day for both temp and pressure.
 
Clarky said:
@Robert. Get the van weighed if you haven't already and then email Continental with the tyre type and size and loaded weights for front and rear axles.

www.continental-tyres.co.uk for more info.

They will give you the correct pressures.

Not sure which van you have but I've recently emailed Michelin for my pressures and have been told to keep 80psi in the rear and 51psi front.
That's for a Carthago Chic C-Line with a max weight of 4500kg.

Richard.
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Hi Richard - I've got the exact same van as you.
Will get it weighed when loaded up and contact Contental

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Southampton said:
I have tyrepal on my tag axle and when I set the rears to 70psi (Michelin Agilis) when they get up to temperature on a run the pressure goes up to about 80psi, when in Spain last year they got up to 85 psi. It's a similar ratio with the fronts. The tyre temps are not excessive maybe 30-35 ish dregs. .......so......when the manufacturers/dealers say to set them to 80psi does this take into account the running pressures??? Or does it not matter?...

I should say this is on a warm day for both temp and pressure.
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Everywhere I've read, tyre pressures are given for COLD tyres, which therefore must take into account the fact that they get hotter when travelling
 
DBK said:
I think this is it. Your tyres are on pages 80 and 81. It is a bit hard to read as you need to look at both pages at the same time!
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Thank you very much!
Just need to find a weigh bridge now
 
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On further investigation I've discovered that the dealer may have deflated my tyres a bit too much as they are currently below even their own 'preferred' figures by about 10psi
I'm going to re inflate them, then to go a weighbridge, to confirm the correct pressure according to Continental
I'm also going to get the wheel alignment checked - recommended annually, as we've been driving on some terrible roads in Italy and hit loads of pot holes.
Hopefully we'll then be set for our next trip in December

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In my Hymer B544 , previous owner has put tp sticker , front 3.2 bar rear 4.5 bar, who are they kidding :doh:

Both Fiat(camping) and Hymer state 5.0 bar all round.

Believe the man who knows (y)
 
I must admit to running our MoHo on lower pressures than those stated as the ride when @80psi is bone crunching, I've gone for 65front 70rear with air bags over the rears set @2bar. It levels it out well when fully loaded.
image.jpg
 
Larrynwin said:
In my Hymer B544 , previous owner has put tp sticker , front 3.2 bar rear 4.5 bar, who are they kidding :doh:

Both Fiat(camping) and Hymer state 5.0 bar all round.

Believe the man who knows (y)
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There is a big difference between different tyre manufacturer's recommendations. The result is the vehicle manufacturer and converter can only give general guidance because they don't know what actual tyres might be fitted after the vehicle is sold. The tyre manufacturer has to be the person who knows what pressures their tyres should be run at.

My 3.5t PVC runs at 3.25 bar all round, using the Continental figures. The handbook says 5.0 bar!
 
DBK said:
There is a big difference between different tyre manufacturer's recommendations. The result is the vehicle manufacturer and converter can only give general guidance because they don't know what actual tyres might be fitted after the vehicle is sold. The tyre manufacturer has to be the person who knows what pressures their tyres should be run at.

My 3.5t PVC runs at 3.25 bar all round, using the Continental figures. The handbook says 5.0 bar!
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Our manufacturers figure was quoted on the exact tyre size and make

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Southampton said:
I have tyrepal on my tag axle and when I set the rears to 70psi (Michelin Agilis) when they get up to temperature on a run the pressure goes up to about 80psi, when in Spain last year they got up to 85 psi. It's a similar ratio with the fronts. The tyre temps are not excessive maybe 30-35 ish dregs. .......so......when the manufacturers/dealers say to set them to 80psi does this take into account the running pressures??? Or does it not matter?...

I should say this is on a warm day for both temp and pressure.
Click to expand...

Hi @Southampton
For the first several months of tag ownership ( Autotrail Chieftain ) I run our rears at 70psi too..

Then I happened to check something in the Autotrail handbook and more or less fell upon the correct pressures recommended for the vehicle

At max load they are supposed to be 55 psi .. I dropped ours down to that and suddenly the van was transformed .. It no longer shook stuff out of cupboards, gripped far better in the wet and all in all behaved better in corners.
Are you SURE you are supposed to be running at those pressures ?
 
Jaws said:
Hi @Southampton
For the first several months of tag ownership ( Autotrail Chieftain ) I run our rears at 70psi too..

Then I happened to check something in the Autotrail handbook and more or less fell upon the correct pressures recommended for the vehicle

At max load they are supposed to be 55 psi .. I dropped ours down to that and suddenly the van was transformed .. It no longer shook stuff out of cupboards, gripped far better in the wet and all in all behaved better in corners.
Are you SURE you are supposed to be running at those pressures ?
Click to expand...

Thanks for the info. When I checked with Michelin, giving them the loaded weights (which were about 50kg under max for all axles) they advised me 70 front and 80 on both rears. 80 was bone rattling so I reduced the rears to 70, not much better though. Was the 55psi in the handbook? I will have a look at that. When you say 55 is that for front and rear?
 
DBK said:
There is a big difference between different tyre manufacturer's recommendations. The result is the vehicle manufacturer and converter can only give general guidance because they don't know what actual tyres might be fitted after the vehicle is sold. The tyre manufacturer has to be the person who knows what pressures their tyres should be run at.

My 3.5t PVC runs at 3.25 bar all round, using the Continental figures. The handbook says 5.0 bar!
Click to expand...

Tyre manufacturers pressure recomendations , as far as I know , are not generally included with new vehicles or provided when replacement tyres are fitted.
This only leaves the vehicle manufacturers recommendations for pressures provided in the hand book and in the door pillar as I am sure most vehicle owners trust this .
I for one would not risk tyre damage/blowout by running pressures 10/15 psi above or below the vehicle manufacturers recommended pressure.
 
Larrynwin said:
Tyre manufacturers pressure recomendations , as far as I know , are not generally included with new vehicles or provided when replacement tyres are fitted.
This only leaves the vehicle manufacturers recommendations for pressures provided in the hand book and in the door pillar as I am sure most vehicle owners trust this .
I for one would not risk tyre damage/blowout by running pressures 10/15 psi above or below the vehicle manufacturers recommended pressure.
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You can of course do what you want and in the absence of anything better you won't be far wrong following what is in the vehicle handbook, which will be generic, catch-all recommendations.

However, if you want to get it perfect you need to check your axle weights and then see what pressures the tyre manufacturer says they should be run at. The one thing you can be certain of is the tyre manufacturer has a better idea than the vehicle manufacturer.

It's been discussed to death on here in the past. :)
 
DBK said:
You can of course do what you want and in the absence of anything better you won't be far wrong following what is in the vehicle handbook, which will be generic, catch-all recommendations.

However, if you want to get it perfect you need to check your axle weights and then see what pressures the tyre manufacturer says they should be run at. The one thing you can be certain of is the tyre manufacturer has a better idea than the vehicle manufacturer.

It's been discussed to death on here in the past. :)
Click to expand...

I completely understand that but of the tens of thousands of new vehicles and new sets of tyres that hit the roads every month , my point was that very few would question the info already provided.

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